AOD, the standard in argon-oxygen decarburization method of producing high-quality stainless and nickel alloy steel has been adopted by steelmakers and foundries because of its advantages over the conventional electric furnace method.

Argon Oxygen Decarburization Treatment

AOD

The Advantages of AOD

Among the major advantages of AOD steelmaking are the increased quality of stainless and the lowered cost per ton. AOD users report the process consistently turns out a quality of stainless that approaches vacuum-degassed material. And many indicate significant savings have been achieved from such AOD factors as: elimination of the need for adding costly low-carbon ferrochrome to the melt; lower operating temperatures and less time necessary in the arc furnace; plus several other time and material savings. Production increases have also been realized by freeing the electric arc furnaces from the refining job. Besides these advantages A0D advocates report the process offers simplicity, flexibility, control and reproducibility far superior to electric furnace practices.

The Argon-Oxygen Process

In the argon-oxygen process, the bath of molten steel receives simultaneous injections of argon or nitrogen and oxygen for decarburization of the melt. Since argon has a cooling effect and oxygen creates heat the temperature of the melt is readily controlled by the amounts of the two gases injected. Nitrogen can be substituted for argon in some grades of stainless, resulting in a savings in argon cost and nitrided ferrochrome or nitrided ferromanganese additions. The process is accomplished in an A0D refining vessel designed especially for this steelmaking method. The steel-shell, refractory-lined A0D vessel, which resembles a Bessemer converter, is mounted on a trunnion for rotating from horizontal to vertical, and is equipped with tuyeres through which the argon and oxygen are injected.

Whiting awarded with building the first AOD vessel

One of the keys to any successful AOD operation is the AOD vessel itself. It must be comparatively lightweight and extremely rugged. Since the process requires frequent changing of the vessels for relining, they must be easily and quickly interchangeable. The job of building the world’s first AOD vessel was awarded to Whiting, a recognized leader in engineering primary metalworking equipment. The Whiting AOD vessel design provides an all-welded, stress-relieved treatment bowl with heavy steel horizontal reinforcing ribs and gusset plates to retain the vessel shape after many heats. The locking arrangement provides quick changeover and allows for expansion between the bowl and trunnion ring. The vessel can be furnished with a completely accessible control panel for regulating gas injections and easily controlling the entire operation of the vessel.

Turnkey Project

Atlas Specialty Steels, Welland, Ontario, Canada

On August 9, 1998, a 70/85 nominal ton AOD converter system poured its first heat at Atlas Specialty Steels, Welland, Ontario, Canada. The system is based upon Praxair’s Argon Oxygen Decarburization (AOD) process for the production of high quality stainless steel, superior castings, low alloy or specialty steels.This turnkey project carried out by Whiting Equipment Canada Inc. proves the high degree of flexibility of the process and its success in meeting the high quality standards set out by Atlas Specialty Steels.

SYSTEM DESCRIPTION

The AOD plant had to be integrated into the existing melt shop, downstream of two (2) operating electric arc furnaces, a VAD all originally supplied by Whiting and a VOD. Pits were not allowed. All equipment had to be built on a mezzanine basis, 24 feet above the plant operating floor. This accounts for the unusual elevation of the tapper’s platform necessary to reach the vessel mouth area and the high piers needed to support the vessel. The tilt drive system is – helical gear, dual-input, single-output, double-quadruple reduction parallel shaft gear drive, connected through a gear coupling and driven by two (2) 52.5 hp dc mill motors. In addition, two (2) nitrogen motors were installed as a backup in case of power failure.